Problem: The number of white balls and red balls in a jar is in the ratio of $3:2$. If there are 9 white balls, how many red balls are there?
For every 3 white balls in the jar, there are 2 red balls in the jar. Since there are 9 white balls in the jar, which is 3 groups of 3 white balls, there must be 3 groups of 2 red balls in the jar. Thus, there are $3\times2 =\boxed{6}$ red balls in the jar.